1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device, and a semiconductor device thus manufactured.
2. Related Art
As a method of electrically isolating adjacent element-forming regions having different potential (device isolation), there has been known a method of forming trenches having the side wall thereof covered with an insulating layer, and then filling the trenches with a polysilicon film or the like. In the process of filling the trenches with the polysilicon film or the like, the polysilicon film is formed over the entire surface of the substrate so as to fill the trenches, and a portion of the polysilicon film which resides over the top surface of the substrate is then removed typically by dry etching.
In the process of filling the trenches with a film, it is generally necessary to form the film to as thick as equal to or more a half of the width of opening of the trenches. On the other hand, at a portion of intersection where the trenches cross, the width of the trenches is substantially wider than the other portions (approximately 1.4 times, if the trenches cross orthogonally). The film formed over the trenches is, therefore, likely to produce a deep recess at the center of the portion of intersection of the trenches. In a later process of forming an insulating film over the substrate, the recess remained unremoved may not completely be filled with the insulating film, instead leaving a void in the insulating film.
A method of suppressing the above-described void has been disclosed, for example, in Japanese Published patent application A-H04-127148. According to this method, an island pattern, which has an area smaller than the portion of intersection of the trenches, is formed in the portion of intersection when the trenches are formed in the substrate.
The present inventor has recognized as follows. The island pattern described in Japanese Published patent application A-H04-127148 will be shrunk, if the design rule of the semiconductor device further shrinks. In this situation, a resist pattern, which is used for forming the island pattern, will have a larger ratio of height relative to the area of base, making itself unstable, and more likely to fall down. The yield of semiconductor device may consequently degrade.